Patent GB-617375-A (GB)
Title: Improvements in or relating to means for actuating the flying controls of aircraft
IPC: B64C13/24
Filed: 1946-09-27
Abstract: 617,375. Fluid-pressure servomotor-control systems. AUTOMOTIVE PRODUCTS CO., Ltd., BLAND, A. N., and DOWN, C. R. Sept. 27, 1946, No. 28927 [Class 135] A fluid-pressure servomotor system for moving a flying control surface of an aircraft comprises servomotors connected to the control surface, two independent sources of pressure fluid and two valves actuated by a common operating member to control the passage of fluid to and from the servomotors, and is arranged so that the extent of movement of the control surface corresponding to a given movement of the operating member is unaffected by failure of either source of pressure fluid and by the sticking of either valve. The control surface 37, Fig. 1, is attached to the raid-point of a yoke 36, pivoted at each end to a double-headed piston 56 in a cylinder fixed to the aircraft frame and divided into four chambers 57 ... 60, the corresponding cylinder chambers being interconnected. The effective surface areas of the pistons exposed to the inner chambers 58, 59, are half those exposed to the outer chambers 57, 60. Two piston valves 42, 43 in fixed cylinders are pivoted to the ends of a yoke 44 centrally attached by a link 45, to a floating lever 46 connected to both the control surface and the pilot's operating member 48. Thus the force required to hold the operating member out of its normal position is proportional to the load on the control surface. The chambers 58, 59 are in direct communication with pressure accumulators 20, 21 respectively. The chambers 57, 60, respectively communicate with a port 72 controlled by a land 61 on the valves 42, 43. Springs 49 tend to hold the yoke 44 perpendicular to the link 45, so that, normally, movement of the operating member produces equal movements of the valves 42, 43, and the lands 61 co-operate with the ports 72 to connect the chambers 57 to either the accumulator 20 or a reservoir 24 and the chambers 60 to either a reservoir 25 or the accumulator 21, thus operating the servomotors and producing a movement of the control surface which acts back through the floating lever 46 to return the valves to their neutral position. In operation, if one valve sticks, the other is moved through twice its normal distance, and lands 63, 64, on the other valve co-operate with ports 77, 75, to connect either an accumulator or a reservoir to a port 76 communicating with the pair of outer chambers normally controlled by the faulty valve. If one piston sticks, the other moves through twice its normal movement before the floating lever follow-up action returns the valves to their neutral position. Failure of one of the sources of pressure fluid renders one half of each servomotor inoperative and unbalances the pressure in the inner chamber of the other half, so that the control surface may be actuated by connecting the operative outer chambers to either the accumulator or the reservoir of the effective source. In a modification, Fig. 8 (not shown), three servomotors, one having twice the effective size of each of the others, are rigidly secured to a bar connected to the control surface and to the movable housings of the valves, and the pilot's operating member is attached to the valve pistons. Thus the pilot is unable to " feel " the load on the control surface and there is no provision for failure of one of the servomotors.